i have searched in more shops and the best prices i can get (and buy) are these:

Sapphire 4850 Normal cooler: ~240 U$D (each one, in these case i will be 2, so 480 U$D the Crossfire)

Sapphire 4850 TOXIC ~260 U$D (so the CrossFire about 500 U$D)

9800GX2 PNY overclocked edition: ~ 380 / 400 U$D

sapphire / His 4870 ~ 380 U$S (in this case it will be only 1 card, but in the future, when the prices Fall, i can buy another one)

Which of this one is the best option to buy? I want to play most of the games with the highest filters AA and AF)

PD: in case that you choose the 4870 and the 4870 extra in the future, Will be my PSU enough for the 4870 CF?? its an ISTAR 750W (from Channel Well technology, its the same engine that the Toughpowers and the Corsair 750W). It only have 2 PCI-e 6 pin plugs